Apparatus for raising the pressure of a fluid



Oct. 15, 1968 FREEMAN 3,405,642

APPARATUS FOR RAISING THE PRESSURE OF A FLUID Filed Nov. 28, 1966 5 Sheets-Sheet l FIG] A. J. M. FREEMAN APPARATUS FOR RAISING THE PRESSURE OF A FLUID Filed Nov. 28, 1966 5 Sheets-Sheet 2 FIG. 7A

Oct. 15, 1968 A. J. M. FREEMAN 3,405,642

APPARATUS FOR RAISING THE PRESSURE OF A FLUID Filed Nov. 28, 1966 5 Sheets-Sheet 3 FIG .2.

United States Patent 3,405,642 APPARATUS FOR RAISING THE PRESSURE OF A FLUID Alan J. M. Freeman, Durham, England, assignor to Olin Mathieson Chemical Corporation, a corporation of Virginia Filed Nov. 28, 1966, Ser. No. 597,458 Claims priority, application Great Britain, Nov. 29, 1965, 50,614/ 65 17 Claims. (Cl. 103-50) ABSTRACT OF THE DISCLOSURE A multi-chambered pump for delivering a fluid to a pressurized environment, a motor for operating the pump, and control means operable to lower the volume of fluid pumped to the pressurized environment upon attainment of a pre-determined load on the motor.

This invention relates to apparatus for raising the pressure of a fluid, and particularly to such apparatus for use at high pressures. Such apparatus includes pumps and intensifiers for liquids and compressors and boosters for gases.

The apparatus hereinafter described has been developed primarily for use inisostatic pressing operations although it has many other applications. In isostatis pressing operations solid particles are enclosed in a bag of rubber which has a predetermined natural shape and the bag is then sealed. The sealed bag is placed in a chamber which is filled with hydraulic liquid and the pressure is then raised to a figure depending on the nature of the solid particles and the desired properties of the final product but frequently of the order of 60,000 lbs. per square inch. The compacted particles are found to form a solid mass conforming to the shape of the rubber bag. High tension ceramic insulators can, for example, be made by this method.

Although liquids such as oil and water are generally regarded as incompressible, they have been found to be compressible at the very high pressures employed using this technique; for example, their compressibility has been found to be of the order of at 30,000 lbs. per square inch and to increase approximately linearly thereafter. The pump which has to pressurise the chamber therefore has to supply a volume of liquid to it. Other factors which may be of importance include the elastic expansion of the container and the reduction in volume due to the compacting of the particles which may be of the order of 80% to 50 depending on the pressure and the particles. It will also be appreciated that very small amounts of air may also present. To build up the pressure to 60,000 lbs. per square inch with a simple pump capable of working up to this pressure would take an unacceptably long time. We therefore aimed to develop a constant stroke pump which works in two or more stages. In the preferred construction according to the invention, the pump is a three stage pump capable of supplying one gallon per minute at pressures up to 2,000 lbs. per square inch, 90 cubic inches per minute at pressures up to 10,000 lbs. per square inch and 16 cubic inches per minute at a pressure of 60,000 lbs. per square inch. The advantage of this arrangement is that the driving head for the pump is more fully used throughout the pressure build-up and the final pressure is reached much more quickly.

Multi-stage hydraulic pumps have been previously proposed but they have not been found to be suitable for use at very high pressures. Moreover, if such pumps had provision for an automatic stage change, this stage change was made in response to the pressure of the pump Patented Oct. 15, 1968 output. Again with the high pressures with which we are mainly concerned, the weakening in the output line caused by the inclusion of a pressure sensitive device brings about a safety problem. Also, it is dilficut to obtain the necessary sensitivity at these high pressures.

I have now found that the stage change can easily be effected in response to the loading of the motor driving the pump. In the case of an air motor, the loading of the motor can be measured through the pressure in the motor chamber and in the case of an electric motor, the loading of the motor can be measured through the current flow. In the case of rotary motors, the torque reaction can be directly measured.

According to the invention there is thus provided apparatus for raising the pressure of a fluid comprising a housing, a member adapted to reciprocate in the housing to compress the fluid in at least two chambers in the housing, a motor for effecting the reciprocation, inlet check valves for the chambers, outlet check valve means for the chambers, and control means for rendering at least one of the inlet check valves ineffective in response to a predetermined loading of the motor in order to reduce the fluid volume delivered per stroke and increase the delivery pressure.

There is further provided apparatus for raising the pressure of a fluid including a drive member mounted for reciprocating movement in a housing and adapted to be moved forward by fluid pressure and back by a spring, the member having a rearwardly extending probe which operates a fluid pressure actuated cycling valve.

The spring return has the advantage that consumption from the pneumatic pressure main is low.

Preferred embodiments of the invention will now be described with reference to the accompanying drawings in which:

FIG. 1 and FIG. 1A are a longitudinal section through a hydraulic pump and motor according to the invention; and

FIG. 2 is a longitudinal section through an alternative form of motor for the pump.

In FIG. 1 the pump itself comprises a main housing 1 having a cylinder in which a reciprocable stepped piston 2 is axially slidable. The smaller diameter portion 3 of the piston 2 has a longitudinal passage and moves over a fixed piston 4 so that three chambers A, B and C are provided, A connector 5 is provided for reciprocating the piston 2 and is connected to a pneumatic motor which will be hereinafter described. The chamber A- is connected to the chamber B through a check valve 6 and a passage 7 through the piston 2; the chamber B is connected through a check valve 8 to the inlet 9; the chamber C is connected to the inlet 9 through a check valve 10; the chamber A is connected through a check valve 15 to the outlet 16; and the chamber C is connected through a check valve 17 to the outlet 16. The check valves 8 and 10 differ from the check valves 6, 15 and 17 in having associated therewith spring loaded tappets 18 and 19 which can be operated to hold them open.

In FIG. 1A the pneumatic motor comprises a motor housing 50 and a cycling valve assembly 51.

The housing 50 comprises two circular dished casing members 52, 53 having flange portions clamped together along their periphery. A piston 55 is mounted on the connector 5 for reciprocating movement in the housing 50 and has a circular seal 54 of U-shaped cross-section. The casing member 53 is secured to the housing 1 and the piston 55 is biased away from the housing 1 by helical compression springs 56, the two springs having different lengths and characteristics. The space behind the piston 55 is connected to the atmosphere through an aperture 57 in the casing member 53 and the space in front of 3 the piston 55 is connected to the valve 51 by a passage 58.

The valve 51 comprises a spool in the form of a differential free piston 60 having a central bore 61 which accommodates a plunger 62, in the form of a central probe attached to the piston 55. The plunger 62 is in sealing engagement with the casing member 52 and the piston 60. The smaller diameter portion of the piston 60 has a sealing ridge 63, which in the position shown (i.e. at the right hand end of its movement) allows the passage 58 to communicate with the chamber P which is connected to the outlet passage 64. The inlet passage 65 leads into the chamber Q on the other side of the ridge 63 and has a side passage 66 leading through a spring loaded control valve 67 to the chamber R. In the position shown, the spring 56 has returned the piston 55 nearly to its extreme rearward position, gas in front of the piston 55 being expelled through the passage 58 and the chamber P. When the plunger 62 reaches the extreme position, it opens the valve 67 so that the pressure in the chamber R rises to the inlet pressure thus moving the piston to the left and connecting the passage 58 to the chamber Q. Gas pressure is thus applied to the piston 55 which commences its return movement so allowing the valve 67 to close. This movement continues until the plunger 62 is no longer sealed in the bore 61. When this occurs, gas passes from the chamber R to the chamber P so that the pressure in the chamber R drops to atmospheric and the pressure in the chamber Q moves the piston 60 to the right, thus permitting gas to be expelled through the passage 58. This cycle is then repeated.

The control means for operating the tappets 18, 19 comprises a linear cam 20 slidably mounted in a body 21. The cam 20 is biassed from right to left against the action of a return spring 22, by means of the mains gas pressure which is applied to the piston 23 Whenever the start valve V is open. This pressure may be of the order of 100 p.s.i. The cam 20 is stopped by a ball latch 24 which engages in a latching groove 25, the groove 25 providing a first abutment surface. A second abutment surface is provided by a second latching groove 26 spaced along the cam 20.

The ball latch 24 is held in a position engaging the cam 20 by a piston rod secured to a piston 27, the piston being spring biassed downwardly by a spring 28 whose compression is adjustable by means of a screw cap 29. The space below the piston 27 is connected to the motor housing 50 in front of the motor piston 55.

The cam 20 has two cam faces 30, 31 for successively depressing balls 35, 36 and thus the tappets 18, 19 as will hereinafter be described. The cam 20 also has two cam rings 33, 34 for engagement with a ball 32 which operates a gas pressure release valve 37 connected to the chamber R of the cycling valve 51.

A conventional pressure regulator 70 may be placed in the pneumatic line between the main start valve V and cycling valve 51.

The pump operates as follows.

It is assumed that the pump is pressurising a container with liquid and that the delivery pressure rises during operation.

The mains air pressure is switched on through the valve V to the cycling valve 51 and the pneumatic motor reciprocates the pump piston 2 with a normally constant stroke.

First stage The tappets 18 and 19 are not depressed and the check valves 8 and 10 can operate in the normal way. On the backwards stroke of the piston 2 liquid is drawn from the inlet 9 through the check valve 8 into the chamber B and some of this liquid is drawn from the chamber B through the passage 7 and the check valve 6 into the chamber A. Simultaneously liquid is drawn through the check valve 10 into the chamber C. During these operations the pressure in the chambers A and C will be low and the check valves 15 and 17 will be held closed. During the forward stroke of the piston 2, the check valves 8 and 10 will close and the check valves, 6, 15 and 17 will open so that liquid from all three chambers is supplied to the outlet 16. (It will be seen that the check valve 6 acts as both the inlet valve for chamber A and the outlet valve for chamber B.) This cycle is then repeated until the pressure at the outlet 16 builds up so that the motor is about to stall.

Stalling will take place when the pressure in front of the piston 55 in the motor housing 50 rises to the value set by the regulator 70. However, the compression of the spring 28 is so arranged that the piston 27 lifts before stalling occurs. The ball latch 24 then disengages from the latching groove 25 under the squeezing action of the pressure exerted on the piston 23 and the cam 20 moves to the left, the cam surface 30 tending to depress the ball 35 and tappet 18 and hold open the valve 8. However, when the cam 20 is released by the latch 24, the piston 2 will be making a delivery stroke so the valve 8 will be held closed by fluid pressure. As the motor might stall before the piston 2 reaches the end of its normal delivery stroke, the valve 37 is provided for ensuring that the piston 2 performs a suction stroke when the tappet 18 is depressed. As the cam 20 moves forward to a position Where the cam face 30 is in contact with the ball 35, the ball 32 is lifted by the cam ring 34 and opens the valve 37. This vents the chamber R so that the piston 60 moves to the right and the suction stroke is immediately begun. This operation relieves the pressure on the piston 27 so that as the cam 20 moves forward to open the now-relieved valve 8 the ball latch 24 engages in the latching groove 26 and the valve 37 closes as the ball 32 drops in behind the cam ring 34.

Second stage In this stage, the tappet 18 is depressed and the check valve 8 is held open. This means that liquid drawn into the chamber B during the backward stroke of the piston 2 is expelled back through the inlet 9 rather than through the outlet 16 during the forward stroke. Thus only the chambers A and C deliver liquid to the outlet 16 and the delivery pressure can be higher without the motor stalling.

When the motor is again about to stall, the gas pressure lifts the piston 27, the ball latch 24 disengages from the groove 26 and the second stage change proceeds in a similar manner to the first stage change described above.

Third stage In this stage, both tappets 18, 19 are depressed so holding the check valve 8, 9 open. The liquid in the chamber C is therefore expelled through the check valve 10 rather than through the check valve 6 during the forward movement of the piston 2. Thus only the chamber A delivers liquid to the outlet 16 and the delivery pressure can again be increased without the motor stalling. When the maximum delivery pressure is reached in the third stage, the motor will stall. When the valve V is turned off so venting the pneumatic system, the spring 22 returns the cam 20 to its starting position.

It will be appreciated that the power output increases to a peak and then drops away during each stage because although the pressure increases throughout, the stroke rate drops. The stage change should desirably take place just after the power peak. The stroke rate is desirably of the order of strokes per minute.

More than three stages could be provided if desired.

Among the advantages of the pump illustrated in FIG. 1 of the drawing are its versatility and the fact that only a limited number of the parts need be made of high grade alloy steel. The use of the plunger 64 to operate the cycling valve 51 has the advantage that the frictional drag of the plunger 62 on the piston 60 tends to reinforce the pneumatically-derived forces holding the piston 60 in its desired position. The coaxial arrangement is also neat and compact.

FIG. 2 illustrates an alternative form of motor piston 55 in which the seal 54 is in the form of a rolling diaphragm. This arrangement reduces the friction loss.

I claim:

1. Apparatus for raising the pressure of a fluid comprising: a housing; a member adapted to reciprocate in said housing to compress the fluid in at least two concentric chambers in said housing; a motor connected to said member and operative to reciprocate said member; inlet check valves in each of said chambers; outlet check valve means in each of said chambers; and control means operatively connected to said motor, said control means being operable to retain at least one of said inlet check valves in an open position in response to an increased loading of said motor to reduce fluid volume delivered per stroke and increase delivery pressure.

2. Apparatus according to claim 1 wherein the motor is a pneumatic motor comprising a motor piston mounted in a motor chamber and adapted to be moved in the di rection which causes delivery of the fluid by gas pressure admitted to the motor chamber, and a cycling valve assembly, and wherein the control means includes pressuresensitive means connected to the motor chamber and adapted to respond to the gas pressure therein, the gas pressure being a measure of the loading of the motor.

3. Apparatus according to claim 2, wherein the motor piston is spring-returned.

4. Apparatus according to claim 3, wherein the motor piston supports a rolling diaphragm secured to the wall of the motor chamber.

5. Apparatus according to claim 2 wherein the cycling valve assembly comprises a pneumatically actuated pilot valve.

6. Apparatus according to claim 5 wherein the motor piston has a control probe for operating the pilot valve.

7. Apparatus according to claim 6 wherein the pilot valve is a spool valve, the spool having a longitudinal passage way through which the probe can move to operate a control valve at one end of the motor piston stroke and through which gas can pass on retraction of the probe to the other end of its stroke.

8. Apparatus according to claim 1 wherein the housing has three chambers in which fluid is compressed by the reciprocating member and wherein the control means is adapted to render t-wo inlet check valves inefiective consecutively to provide three delivery stages of decreasing delivery volume per stroke and increasing delivery pressure.

9. Apparatus according to claim 8 wherein the control means is adapted to be biassed in a direction tending to for holding open the inlet check valves successively operable by the cam means.

10. Apparatus according to claim 9 wherein the cam means is adapted to be biased in a direction tending to hold open the inlet check valves and the control means includes stop means permitting the cam means to move successively in two stages.

11. Apparatus according to claim 10 wherein the cam means has two longitudinally spaced abutment surfaces thereon for successive engagement with the stop means, the stop means withdrawing when the motor reaches the predetermined loading.

12. Apparatus according to claim 11 wherein means are provided for automatically ensuring that the reciprocating member operates a suction stroke when the tappet is depressed.

13. Apparatus according to claim 12 wherein the motor is a pneumatic motor provided with a cycling valve assembly and wherein said means comprises a pressure release valve operable by the cam means and connected to the cycling valve assembly.

14. Apparatus according to claim 8 wherein the reciprocating member is a stepped piston which co-operates with the housing to form two of the chambers and which has a longitudinal passage therein forming the third chamber, a fixed piston being mounted in the housing so that the stepped piston moves over it.

15. Apparatus according to claim 14 wherein a check valve in the piston acts as an inlet check valve for the third chamber and is connected to one of the first two chambers for which it acts as an outlet check valve.

16. A pneumatic motor for use in raising the pressure of a fluid comprising: a motor housing; a piston mounted for reciprocating motion in said motor housing; a cycling valve assembly connected to said motor housing, said valve assembly comprising a valve housing; a pneumatically actuated valve spool having a longitudinal passage extending therethrough, said spool being mounted for reciprocating motion in said valve housing; a control valve for controlling the admission of air to a chamber bounded by an end of said spool remote from said piston; and a probe mounted on said piston and adapted to pass through said passage in sealing engagement therewith, said probe being operable to open said control valve at one end of its stroke and to open said pasasge at the other end of its stroke.

17. The motor of claim 16, further comprising a rolling diaphragm secured to a wall of said motor chamber and supported by said piston.

References Cited UNITED STATES PATENTS 1,703,003 2/1929 Harteau 230-52 1,864,132 6/1932 Halleck 230-26 2,401,827 6/ 1946 Heitchue 23026 XR 2,698,710 1/1955 Pedroia 230-52 3,162,132 12/1964 Kling 103-60 ROBERT M. WALKER, Primary Examiner.

US. DEPARTMENT OF COMMERCE PATENT OFFICE Washington, D.C. 20231 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,405,642 October 15, 1968 Alan J. M. Freeman It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below: Column 1, line 27, "inisostatic" should read in isostati Column 5, line 49, beginning with "9. Apparatus" cancel all to and including "means." in line 52, same column 5, and insert 9. Apparatus according to claim 8 wherein the control means includes linear cam means and respective tappets for holding open the inlet check valves successively operable by the cam means.

Signed and sealed this 24th da of February 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

